Systems and methods of open contention-based grant allocations

ABSTRACT

A method may include transmitting an open contention-based grant to optical network units (ONUs) and receiving, from at least one of the ONUs, a response to the open contention-based grant. The method may also include determining whether a collision has occurred in response to the open contention-based grant. The method may further include provisioning grants to ONUs in response to determine that a collision has occurred

RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.16/928,237, entitled “Systems and Methods of Open Contention-Based GrantAllocations” and filed Jul. 14, 2020, which claims priority under 35U.S.C. § 119 based on U.S. Provisional Application 63/010,194 entitled“Systems and Methods of Open Contention-Based Grant Allocation toIncrease Effective Upstream Service Capacity in a Passive OpticalNetwork,” filed Apr. 15, 2020, the contents of which are both herebyincorporated herein by reference in their entireties.

BACKGROUND

A Passive Optical Network (PON) is an optical access network that istypically based on a point-to-multipoint (P2MP) optical fiber topology,known as an optical distribution network (ODN). An ODN uses fiber andpassive components, such as splitters and combiners. A PON system usesthe ODN to provide connectivity between a number of central nodes and anumber of user nodes using bi-directional wavelength channels. Operationof the PON system in the upstream direction from user nodes to thecentral nodes typically utilizes principles of Time-Division MultipleAccess (TDMA) for each wavelength channel. For example, each user nodeis granted or allocated an upstream transmission opportunity within atightly controlled time interval.

In response to a grant of a transmission opportunity, also referred toas an allocation, a user node turns on its optical transmitter,transmits a burst of data along with Operations and Maintenance (O&M)information, and then turns off its transmitter until the nexttransmission opportunity is granted. The frequency and size of grants toan individual user node is arbitrated by a central node. The centralnode operates under multiple constraints associated with the individualuser node's service rate, delay, and jitter requirements. Increasing thefrequency of the transmission opportunities granted to an individualuser node allows that user node to transmit upstream bursts more oftenand improves the delay and jitter performance of that particular usernode. However, each transmitted burst from the user node incurs anoverhead. Such overhead reduces the overall available upstream databandwidth in the PON.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary multi-channel PON system in whichsystems and methods described herein may be implemented;

FIG. 2 is a block diagram of a burst transmission in accordance with anexemplary implementation;

FIG. 3 is a block diagram of components implemented in one or more ofthe elements illustrated in FIG. 1 in accordance with an exemplaryimplementation;

FIG. 4 is a block diagram of components implemented in the optical lineterminal channel termination (OLT CT) device of FIG. 1 in accordancewith an exemplary implementation;

FIGS. 5A and 5B are flow diagrams illustrating processing associatedwith the environment of FIG. 1 in accordance with an exemplaryimplementation;

FIG. 6 is a flow diagram illustrating processing associated with acleared collision in accordance with an exemplary implementation; and

FIG. 7 is an exemplary timing diagram associated with the use of an opencontention-based grant in accordance with an exemplary implementation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description refers to the accompanying drawings.The same reference numbers in different drawings may identify the sameor similar elements.

Implementations described herein provide systems and methods forgranting upstream transmission opportunities on a contention basis, thusreducing the upstream overhead while meeting the delay and jitterrequirements of individual nodes. For example, in one implementation, abroadcast contention-based grant in a PON system, referred to herein asan open upstream transmission grant or open contention-based grant, maybe used. The open upstream transmission grant is broadcast and can beutilized by any active pre-ranged optical network unit (ONU). Incontrast to conventional unicast directed grants, an open upstreamtransmission grant may receive a response from multiple ONUs. Further,in contrast to conventional contention-based serial number grants, anopen upstream transmission grant does not require a quiet window that isused to avoid collisions. The term “collision” as used herein refers totransmissions from two or more ONUs that overlap in time from theperspective of a receiver device, such as an optical line transmitterchannel termination (OLT CT) device, that receives the transmissions. Asa result, using open upstream transmission grants may increase systemthroughput, while also meeting user nodes' service rate, delay andjitter requirements.

FIG. 1 illustrates an exemplary environment 100 in which systems andmethods described herein may be implemented. Environment 100 includes amulti-channel time wavelength division multiplexing (TWDM) system thatincludes a number of optical line terminal channel termination (OLT CT)devices 110-1 through 110-N, wavelength multiplexer (WM) 120, opticaldistribution network (ODN) 130 and optical network units (ONUs) 140-1through 140-N.

OLT CT devices 110 (referred to individually as OLT CT 110 or OLT CT110-x, and collectively as OLT CTs 110) each include an optical devicethat may perform various functions, such as traffic scheduling, buffercontrol and bandwidth allocation. In an exemplary implementation, eachOLT CT 110 is associated with its own bi-directional wavelength channelhaving a fixed downstream wavelength and a fixed upstream wavelength.OLTs 110 may be connected to WM 120 via channel drop fibers 112. In anexemplary implementation, OLT CT 110 controls upstream transmissionsfrom ONUs 140 via a Bandwidth Map (BWmap). For example, OLT CT 110 maygenerate the BWmap based on a number of inputs and transmit the BWmapvia WM 120 and PON 130 to ONUs 140, as described in detail below.

ODN 130 includes an optical network that provides an opticaltransmission medium between, for example, OLT CTs 110 and ONUs 140. Forexample, ODN 130 may include optical splitter 132 and optical fibers134. ODN 130 may also include fiber optic connectors, attenuators,modulators and other optical components (not shown). In an exemplaryimplementation, ODN 130 may include a passive optical distributionnetwork that includes no active components that are used to transmitsignals through ODN 130. In other implementations, ODN 140 may includeactive optical network components, such as optical amplifiers, switches,multiplexers, etc.

ONUs 140 (referred to individually as ONU 140 or ONU 140-x, orcollectively as ONUs 140) may each include an optical device thatprovides network-side line termination and user-side line termination.For example, ONU 140 may perform various functions, such as convertingan optical signal to an electrical signal and multiplexing andde-multiplexing. ONU 140 may connect to various end devices or userdevices (not shown). For example, the end devices may executeapplications and provide users with access to various services, such astelevision service, telephone service, Internet service and/or othertypes of services.

In accordance with an exemplary implementation, each ONU 140 may choosea single wavelength channel via which to operate and a single OLT CT 110as a central node with which ONU 140 will communicate and receiveinstructions. ONU 140 may also switch wavelength channels, as instructedby the respective OLT CT 110. In addition, and in accordance with anexemplary implementation, an optical transmitter at OLT CT 110 operatesin a continuous wave (CW) mode and an optical transmitter at ONUs 140operates in a burst mode (BM).

The exemplary configuration illustrated in FIG. 1 is provided forclarity. It should be understood that a typical environment may includemore or fewer devices than illustrated in FIG. 1. For example,environment 100 may include a large number (e.g., hundreds or more) ofONUs 140, as well as a large number of OLT CTs 110. Environment 100(e.g., PON 130) may include additional splitters and network devicesthat aid in routing data in environment 100.

Various operations are described below as being performed by particularcomponents in environment 100. In other implementations, variousoperations described as being performed by one device may be performedby another device or multiple other devices, and/or various operationsdescribed as being performed by multiple devices may be combined andperformed by a single device.

As described above, ONUs 140 may operate in burst mode to transmit data.FIG. 2 illustrates an exemplary burst transmitted by an ONU 140.Referring to FIG. 2, burst 220 may include preamble 240, delimiter 250and data payload 260. Preamble 240 and delimiter 250, along with theguard time that accommodates Enable Transient time 210 and DisableTransient time 230, correspond to physical layer overhead during burstmode operation. The timing of burst 220 may be tightly controlled by thePON TWDM protocol used in environment 100. For example, the opticaltransmitter at ONU 140 is normally in an OFF state, with the emittedoptical power at or close to zero, as illustrated at line 205 in FIG. 2.Once the transmitter at ONU 140 is enabled by the rising edge 265 ofTransmit Enable signal 270, the transmitter takes the Enable Transienttime 210 to reach the operation state. The transmitter at ONU 140 thentransmits burst 220, which may be a modulated optical signal, until thefalling edge 275 of Transmit Enable signal 270 causes the transmitter tostop transmitting the burst and to return to the OFF state within theDisable Transient time 230.

As discussed above, the upstream transmission burst 220 may includepreamble 240, delimiter 250 and payload 260. Preamble 240 allows theremote end optical receiver at OLT CT 110 to perform clock and datasignal amplitude recovery. Delimiter 250 allows the remote end opticalreceiver at OLT CT 110 to delineate the start of the data transmission.Data payload 260 includes a burst header and burst payload. Burst 220may be transmitted by ONUs 140 in response to open contention-basedgrants, as described in detail below. The term “open contention-basedgrant,” or “open upstream grant,” as used herein should be construed asa broadcast grant that does not require a quiet window and can beresponded to by multiple ONUs 140.

FIG. 3 illustrates an exemplary configuration of a device 300. Device300 may correspond to or include elements implemented in components ofenvironment 100, such as OLT CTs 110, a component of OLT CT 110 (e.g., abandwidth assignment module/logic, a bandwidth map generationmodule/logic, etc.), ONUs 140, etc. Referring to FIG. 3, device 300 mayinclude bus 310, processor 320, memory 330, input device 340, outputdevice 350 and communication interface 360. Bus 310 may include a paththat permits communication among the elements of device 300.

Processor 320 may include one or more processors, microprocessors, orprocessing logic that may interpret and execute instructions. Memory 330may include a random access memory (RAM) or another type of dynamicstorage device that may store information and instructions for executionby processor 320. Memory 330 may also include a read only memory (ROM)device or another type of static storage device that may store staticinformation and instructions for use by processor 320. Memory 330 mayfurther include a solid state drive (SSD). Memory 330 may also include amagnetic and/or optical recording medium (e.g., a hard disk) and itscorresponding drive.

Input device 340 may include a mechanism that permits a user to inputinformation, such as a keyboard, a keypad, a mouse, a pen, a microphone,a touch screen, voice recognition and/or biometric mechanisms, etc.Output device 350 may include a mechanism that outputs information tothe user, including a display (e.g., a liquid crystal display (LCD)), aprinter, a speaker, etc. In some implementations, a touch screen displaymay act as both an input device and an output device.

Communication interface 360 may include one or more transceivers thatdevice 300 uses to communicate with other devices via wired, wireless oroptical mechanisms. For example, communication interface 360 may includeone or more optical or radio frequency (RF) transmitters, receiversand/or transceivers and one or more components and/or antennas fortransmitting and receiving optical data, RF data, etc. Communicationinterface 360 may also include a modem or an Ethernet interface to a LANor other mechanisms for communicating with elements in a network.

The exemplary configuration illustrated in FIG. 3 is provided forsimplicity. It should be understood that device 300 may include more orfewer devices than illustrated in FIG. 3. In an exemplaryimplementation, device 300 performs operations in response to processor320 executing sequences of instructions contained in a computer-readablemedium, such as memory 330. A computer-readable medium may be defined asa physical or logical memory device. The software instructions may beread into memory 330 from another computer-readable medium (e.g., a harddisk drive (HDD), solid state drive (SSD), etc.), or from another devicevia communication interface 360. Alternatively, hard-wired circuitry maybe used in place of or in combination with software instructions toimplement processes consistent with the implementations describedherein. Thus, implementations described herein are not limited to anyspecific combination of hardware circuitry and software.

FIG. 4 is a block diagram of components implemented in OLT CT 110 inaccordance with an exemplary implementation. Referring to FIG. 4, OLT CT110 includes bandwidth assignment logic 410, bandwidth map generationlogic 420, traffic monitoring logic 430, allocation identifier (ID)table 440, collision detection logic 450, priority list 460 andcommunication logic 460. These elements may be implemented by processor320 executing instructions stored in memory 330 of OLT CT 110. Inalternative implementations, these components or a portion of thesecomponents may be located externally with respect to OLT CT 110.

Bandwidth assignment logic 410 may include logic to assign bandwidth toONUs 140. Bandwidth assignment logic 410 may assign bandwidth based on,for example, transmission container (T-CONT) traffic descriptorconfigured rate parameters for particular ONUs 140, dynamic T-CONTactivity/traffic monitoring information, etc. Bandwidth assignment logic410 may also identify service level agreements (SLAs) associated withparticular ONUs 140 to generate bandwidth assignments. In each case,bandwidth assignment logic 410 may generate values of assignedbandwidths for each traffic flow identified by an Allocation ID.Bandwidth assignment logic 410 may generate a set of assigned bandwidthsfor a certain time period and forward the assigned bandwidths tobandwidth map generation logic 420.

Bandwidth map generation logic 420 may include logic to generate abandwidth map (BWmap) and transmit the BWmap to ONUs 140. Bandwidth mapgeneration logic 410 may receive inputs, such as T-CONT trafficdescriptor configured timing parameters, upstream physical layerOperations, Administration and Maintenance (PLOAM)information/indicators, assigned bandwidths from bandwidth assignmentlogic 410 to generate BW map. In accordance with an exemplaryimplementation, bandwidth map generation logic 420 may also receiveinformation indicating whether an open grant collision has been detectedand a list of ONUs 140 that are subject to directed grant suppression.Bandwidth map generation logic 420 may use the open grant collisionindication and the list of suppressed ONUs 140 when generating BWmaps atregular intervals, as described in detail below.

Traffic monitoring logic 430 may include logic to monitor dynamic T-CONTactivity in environment 100 (e.g., on PON 130). For example, trafficmonitoring logic 430 may identify overall data traffic/throughput,status information such as whether a particular ONU 140 is receivingadequate bandwidth, etc.

Allocation ID table 440 may store a database of allocation IDs for usein environment 100. In accordance with an exemplary implementation, oneor more allocation IDs associated with broadcasting may be reserved toprovide for open contention-based allocations that may be used byeligible ONUs 140.

Collision detection logic 450 may include logic to identify when two ormore ONUs 140 have transmitted data at the same time or in overlappingtime intervals, resulting in a collision. For example, collisiondetection logic 450 detects collisions in timeslots corresponding toopen contention-based grants. As an example, collision detection logic450 may detect a collision within an open contention-based time slot bymonitoring the level of optical power received by OLT CT 110. In thiscase, collision detection logic 450 may identify whether the receiver atOLT CT 110 fails to recover the clock and data associated with a bursttransmission, fails to delineate a burst based on a received deli meter(e.g., delimiter 250), determines an abnormal error level as provided bya hybrid error correction (HEC) indication, bit-interleave parity (BIP)error indication and/or forward error correction (FEC) indication.Collision detection logic 450 may also identify collisions via othermechanisms.

Suppressed ONU list 460 may include a list of ONUs 140 that are subjectto directed grant suppression. Such ONUs 460 may be associated with enddevices/applications that are not expected to respond to allocations atregular intervals and/or do not need to respond to each allocation. Forexample, ONUs 140 supporting monitoring applications that arecharacterized by very low bandwidth requirements, such as intrusiondetection applications, medical monitoring, etc., that may not beexpected to respond to allocations at regular intervals. However, theseapplications may have stringent reporting/delay time requirements.

As another example, an ONU 140 may be working on a different channel,but OLT CT 110 may provide a protection channel for that ONU 140. Forexample, in a multi-wavelength PON system, such as Next generation PONPhase 2 (NG-PON2), a wavelength channel which carries bi-directionaluser traffic of its own, may be used for protection of the ONUs 140 onanother wavelength channel which support mission-critical services(e.g., services that require quick restoration time in case of aprotection event, such as service level agreement (SLA)-based businessservice or wireless transport). In order to meet the restoration timerequirements, in one embodiment, an ONU 140 may have an opportunity totransmit a burst within a short time of a protective wavelengthswitching event that can occur at a random, unpredictable instance. TheONU 140 may be pre-ranged in the protection channel due to consistentranging methodology. In this case, OLT CT 110 may provide directedgrants to each protected ONU 140 at a high frequency, whereas thosegrants would normally be unused (zero useful data transmitted), with theexception of the occurrence of protective wavelength switching events.

As still another example, an OW 140 may be in a power savings mode formost of the time and execute a standard-based Watchful Sleep protocoland abstain from responding to the directed grants to save power, unlessthe OLT CT 110 provides a Forced wake-up indication, or a local stimulusevent that causes the ONU 140 to resume operation in full power. Oncethe ONU 140 is placed in the Low Power state, OLT CT 110 may continue toprovide regular upstream transmission grants to the ONU 140 to supportits ability to wake up on a local stimulus and to indicate itswillingness to resume full-power operation. Unless the ONU 140 observesa local wake-up stimulus, these grants remain unused.

ONU list 460 may include a list of such ONUs 140 for which direct grantallocations may be suppressed. That is, such ONUs 140 may not receiveany directed grants from OLT CT 110. In accordance with an exemplaryimplementation, suppressed ONU list 460 may be partitioned into two ormore priority sections, such as high priority, average priority and lowpriority.

Communication logic 470 may include logic for communicating with devicesin environment 100. For example, communication logic 470 may include anoptical transceiver that transmits and receives optical informationto/from PON 130. Communication logic 470 may communicate with WM 120 andother devise in environment 100.

Although FIG. 4 shows exemplary components of OLT CT 110, in otherimplementations, OLT CT 110 may include fewer components, differentcomponents, differently arranged components, or additional componentsthan depicted in FIG. 4.

As described above, implementations described herein provide an openupstream transmission grant that may be broadcast from OLT CT 110 to anumber of ONUs 140. The open upstream transmission grant may be utilizedby any active pre-ranged ONU 140. In contrast to unicast directedgrants, an open upstream transmission grant may receive a response frommultiple ONUs 140. In addition, in contrast to contention-based serialnumber grants, an open upstream transmission grant does not require aquiet window, but rather a regular guard time interval. The OLT CT 110may utilize the open upstream transmission grant in place of multiplehigh-frequency directed grants to multiple individual ONUs 140, each ofwhich is unlikely to respond to the grant, thus substantially improvingthe upstream service capacity.

In an exemplary implementation, the open upstream transmission grantsmay be identified by the special reserved values of Alloc-ID, which donot coincide with the Alloc-ID values reserved for any other purpose. AnONU 140 which has been activated and ranged may utilize an open upstreamtransmission grant to communicate signaling or data information to theOLT CT 110. When the OLT CT 110 receives a response to an open upstreamtransmission grant from a particular ONU 140, OLT CT 110 may restorethat ONU 140's directed grants allocated on the individual basis andfollow an appropriate signaling and/or data exchange protocol that isbeing executed.

When OLT CT 110 detects a collision within the time interval whichcorresponds to an open upstream transmission grant, OLT CT 110 performsone or both of the following: OLT CT 110 increases the frequency of theopen upstream transmission grants; OLT CT 110 restores one or more ONUs140 whose individual directed upstream transmission grants have beensuppressed/withdrawn or reduced in frequency in favor of the openupstream contention-based transmission grants.

FIGS. 5A and 5B are flow diagrams illustrating processing in accordancewith an exemplary implementation. Processing may begin with OLT CT 110ranging ONUs 140 (FIG. 5A, block 510). For example, during provisioningassociated with environment 100, OLT CT 110 may transmit a ranging grantto ONU 140-1 and measure the round-trip time for a data transmissionfrom OLT CT 110 to ONU 140-1 and back to OLT CT 110. OLT CT 110 may thencalculate an equalization delay for ONU 140-1 (block 510). Theequalization delay is based on the length of the optical fibers (e.g.,optical fibers 112, 122 and 134) connecting OLT CT 110 to ONU 140. OLTCT 110 may transmit ranging grants and determine the equalization delayfor each ONU 140 in a similar manner. Once each ONU 140 has been rangedand an equalization delay has been determined, ONUs 140 may be capableof responding to an open-contention based grant, as described below.

Processing may continue with OLT CT 110 receiving transmission container(T-CONT) descriptor rate parameters (block 520). For example, bandwidthassignment logic 410 may receive T-CONT descriptor rate parametersduring provisioning of OLT CT 110 by the service provider associate withenvironment 100. In an exemplary implementation, the T-CONT descriptorrate parameters may identify a fixed rate, an assured rate and/or amaximum rate. The fixed rate identifies the transmission rate to beprovided to ONUs 140 at any time, regardless of whether each ONU 140 hasdata to transmit. The assured rate identifies the rate at which each ONU140 will be able to transmit data when ONU 140 has data to transmit. Themaximum rate identifies a maximum rate provided to an ONU 140, such aswhen no other ONUs 140 in environment 100 have data to transmit.

OLT CT 110 may also receive T-CONT descriptor timing parameters (block520). For example, bandwidth map generation logic 420 may receive T-CONTdescriptor timing parameters during service provisioning from theservice provider. The timing parameters may include, for example, jittertolerance/requirements associated with ONUs 140.

OLT CT 110 may also receive dynamic T-CONT activity indicationsassociated with traffic in environment 100 (block 530). For example,traffic monitoring logic 430 may receive traffic load information,traffic status reports, etc., associated with traffic in environment100. Traffic monitoring logic 430 may forward the traffic information tobandwidth assignment logic 410. OLT CT 110 may also generate bandwidthassignments for ONUs 140 (block 540). For example, based on the receivedT-CONT descriptor rate parameters and the dynamic traffic activity,bandwidth assignment logic 410 may provide bandwidth assignments foreach ONU 140. Bandwidth assignment logic 410 may then forward thebandwidth assignment information to bandwidth map generation logic 420.In accordance with an exemplary implementation, bandwidth assignmentlogic 410 may forward the bandwidth assignment information at regularintervals (e.g., every millisecond (ms) or some other period).

During initial provisioning of OLT CT 110 or in the course of regularoperation, OLT CT 110 may also receive upstream physical layerOperations, Administration and Maintenance (PLOAM) information. Forexample, the service provider associated with environment 100 mayidentify the amount of PLOAM information that may be included in databursts sent from ONUs 140 and provide this information to bandwidth mapgeneration logic 420. OLT CT 110 may also use this information whendecoding bursts from ONUs 140.

Bandwidth map generation logic 420 may generate a bandwidth map (BWmap)based on the received information (block 550). For example, bandwidthmap generation logic 420 may generate the bandwidth map based on thereceived bandwidth assignments from bandwidth assignment logic 410, thereceived T-CONT descriptor timing parameters and the upstream PLOAMinformation. Bandwidth map generation logic 420 may also use anindication of whether a collision has occurred and the list ofsuppressed ONUs 140 when generating BWmap, as described in more detailbelow.

Bandwidth map generation logic 410 may broadcast the BWmap to ONUs 140(block 550). For example, in accordance with an exemplaryimplementation, bandwidth map generation logic 410 may broadcast BWmapevery predetermined period of time, such as every 125 microseconds (μs).OLT CT 110 may monitor the network in accordance with each BWmap todetermine whether an upstream open grant collision is detected (block560). For example, as discussed above, collision detection logic 450 maydetermine that the receiver at OLT CT 110 has failed to recover theclock and data associated with a burst transmission, failed to delineatea burst based on a received delimeter 250, determined an abnormal errorlevel as provided by a hybrid error correction (HEC) indicationbit-interleave parity (BIP) error indication and/or forward errorcorrection (FEC) indication, etc. Assume that OLT CT 110 receives aresponse to an open upstream transmission grant from one particular ONU140 and no collision is detected (block 560—no). That is, OLT CT 110detected optical power on the particular channel, received the opticaltransmission via its receiver, and successfully decoded the transmission(e.g., detect the delimiter 250, identified the header information,identified and successfully decoded the payload, etc.). In this case,OLT CT 110 continues to monitor environment 100 and generates the nextBWmap at the predetermined time (block 570).

If, however, OLT CT 110 detects a collision within the time intervalwhich corresponds to an open upstream transmission grant (block560—yes), OLT CT 110 may access suppressed ONU list 460 (FIG. 5B, block580). As discussed above, suppressed ONU list 460 may include variousONUs 140 that may not be able to or may not need to respond to thebandwidth allocations provided by OLT CT 110. Such reasons may include,for example, ONUs 140 that are primarily devoted to monitoringapplications which only need to report an infrequent abnormal event,ONUs 140 being served on a different channel in a multi-wavelength PONsystem, and are offered wavelength protection by the given channel, ONUs140 that are executing a standard-based power saving protocol andabstain from responding to the grants to conserve power, etc.

OLT CT 110 may also determine if a priority list or priority informationis present in suppressed ONU list 460 (block 585). For example,suppressed ONU list 460 may include priority information associated withONUs 140 for which directed grants have been suppressed. The priorityinformation may include a relative priority, such high priority, mediumpriority, low priority.

If a priority list/information is present (block 585—yes), OLT CT 110may restore or reinstate one or more ONUs 140 whose individual regulardirected upstream transmission grants have been suppressed or reduced infrequency (block 590). Additionally, or alternatively, OLT CT 110 mayincrease the frequency of the open contention-based upstreamtransmission grants (block 595). If no priority list/information ispresent (block 585—no), OLT CT 110 may increase the frequency of theopen contention-based upstream transmission grants (block 595). In thismanner, when a collision occurs, OLT CT 110 may take actions to ensurethat ONUs 140 having information to transmit will be able to effectivelytransmit the information via additional open-contention based grantsand/or dedicated grants.

In some implementations, if suppressed ONU list 460 does not includepriority information, OLT CT 110 may restore directed grants to all ONUson suppressed ONU list 460. In each case, after the previouslysuppressed ONUs 140 and ONUs 140 which transmitted data that resulted incollisions have been given the opportunity, such as a period of time totransmit data via directed grants and/or the increased frequency of theopen-contention based grants, OLT CT 110 may determine if the collisionhas been cleared.

FIG. 6 illustrates exemplary processing associated with clearedcollisions. Processing may begin with OLT CT 110 determining if the opengrant collision has been cleared (block 610). For example, collisiondetection logic 450 may determine whether any collision is currentlydetected. If an open grant collision has not been cleared (i.e., acurrent collision is detected) (block 610—no), OLT CT 110 may continueto operate with directed grants to ONUs 140 on the suppressed ONU list460 and/or increased frequency of open contention-based grants.

If, however, the open grant collision has been cleared (block 610—yes),OLT CT 110 may suppress directed grants to ONUs 140 on the suppressedONU list 460 having the appropriate priority (block 620). Alternatively,OLT CT 110 may suppress directed grants to all ONUs 140 on thesuppressed ONU list 460. Additionally or alternatively, OLT CT 110 mayalso decrease the frequency of open contention-based grants to a normallevel (e.g., the frequency prior to detection of the collision) (block630). In this manner, once an open-contention based collision has beencleared, OLT CT 110 may generate and transmit BWmaps that allow each ONU140 to transmit data, while increasing data throughput.

As discussed above, open contention-based grants may allow ONUs 140 totransmit data without requiring a quiet window. FIG. 7 illustrates anopen contention-based grant in accordance with an exemplaryimplementation. As described previously, open contention-based grantsmay be addressed to ranged ONUs 140 for which an equalization delay(EQD) have been assigned.

Referring to FIG. 7, the broadcast open contention-based grant isspecified by the Start Time (ST) and the Grant Size (GS). Upon receivingthe BWmap from OLT CT 110, any ONU 140 which is the member of thespecified recipient set (e.g., ONUs 140-1, 140-2, 140-3 and 140-4 inthis example) may respond to the grant with a delay ST+EqDx, where xcorresponds to any integer associated with ONUs 140-1 through 140-N. OLTCT 110 expects a response to a broadcast open contention-based grant tostart arriving at time t₀+T_(z)+ST_(X). As discussed above, a collisionbetween two or more ONU 140 responses is possible, if two or moremembers of the ONU 140 recipient set, such as ONU 140-2 and 140-3 inthis example, choose to respond to the same grant. In such cases, theprocessing described above will be performed to resolve the collisionsand maintain data throughput.

Implementations described herein provide open contention-based upstreamgrants to ONUs 140 without requiring a quiet window. This may allow ONUs140 to utilize open upstream transmission grant, as opposed to usingmultiple high-frequency directed grants to multiple individual ONUs140.In situations in which particular ONUs 140 are unlikely to respond todirected grants, the use of open contention-based grants substantiallyimproves the upstream service capacity. In addition, as state-of-the-artPON systems evolve towards new advanced applications with large numberof users with widely ranging heterogeneous service requirements in termsof data rate, latency, jitter, and quality of service (QoS) guarantees,using open contention-based grants allows the PON system to increaseoverall capacity and meet the users' service requirements.

The foregoing description of exemplary implementations providesillustration and description, but is not intended to be exhaustive or tolimit the embodiments to the precise form disclosed. Modifications andvariations are possible in light of the above teachings or may beacquired from practice of the embodiments.

For example, features have been described above with respect to OLT CT110 providing BWmaps based on particular input and at predeterminedtimes. In other implementations, other devices in environment 100 may beused to provide BWmap information.

Further, in some implementations, in order to optimize the averagecollision resolution time, once an ONU 140 uses an open contention-basedgrant, that ONU 140 may be configured to skip responding to apredetermined or random number of future open contention-based grants orskip responding to future open contention-based grants for a period oftime. In addition, in some implementations, if an ONU 140 receives adirected grant, that ONU 140 may be configured to not respond to apredetermined or random number of future open contention-based grants ornot be eligible to respond to open contention-based grants for a periodof time.

Still further, while series of acts have been described with respect toFIGS. 5A, 5B and 6, the order of the acts may be different in otherimplementations. Moreover, non-dependent acts may be implemented inparallel.

It will be apparent that various features described above may beimplemented in many different forms of software, firmware, and hardwarein the implementations illustrated in the figures. The actual softwarecode or specialized control hardware used to implement the variousfeatures is not limiting. Thus, the operation and behavior of thefeatures were described without reference to the specific softwarecode—it being understood that one of ordinary skill in the art would beable to design software and control hardware to implement the variousfeatures based on the description herein.

Further, certain portions of the invention may be implemented as “logic”that performs one or more functions. This logic may include hardware,such as one or more processors, microprocessor, application specificintegrated circuits, field programmable gate arrays or other processinglogic, software, or a combination of hardware and software.

In the preceding specification, various preferred embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe broader scope of the invention as set forth in the claims thatfollow. The specification and drawings are accordingly to be regarded inan illustrative rather than restrictive sense.

No element, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly described as such. Also, as used herein, thearticle “a” is intended to include one or more items. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. A method, comprising: receiving, from at leastone of a plurality of optical network units (ONUs), a response to anopen contention-based grant; determining whether a collision hasoccurred in response to the open contention-based grant; andprovisioning grants to ONUs in response to determining that a collisionhas occurred, wherein the provisioning comprises at least one of:increasing a frequency of open-contention based grants for a period oftime after the collision occurred, or providing directed grants toselected ONUs for the period of time after the collision occurred. 2.The method of claim 1, wherein the provisioning grants comprises:increasing the frequency of open-contention based grants for the periodof time after the collision occurred.
 3. The method of claim 1, whereinthe provisioning grants comprises: providing directed grants to selectedONUs for the period of time.
 4. The method of claim 1, wherein theprovisioning grants comprises: providing directed grants to the selectedONUs based on types of devices coupled to the ONUs or applicationsexecuted by the devices coupled to the ONUs.
 5. The method of claim 4,wherein the providing directed grants further comprises: providingdirected grants to the selected ONUs based on an amount of bandwidth thedevices or applications are expected to use.
 6. The method of claim 1,wherein the provisioning grants comprises providing directed grants tothe selected ONUs, and wherein the providing directed grants comprises:identifying a priority associated with at least some of the ONUs, andproviding the directed grants to the at least some of the ONUs based onthe priority.
 7. The method of claim 1, further comprising: determiningthat the collision has occurred; determining whether the collision hasbeen cleared; and at least one of: decreasing a frequency ofopen-contention based grants for future periods of time in response todetermined that the collision has been cleared, or suppressing directedgrants to selected ONUs in response to the determining that thecollision has been cleared.
 8. The method of claim 1, furthercomprising: generating a bandwidth map, wherein the bandwidth map isbased on whether a collision has occurred and a list of ONUs for whichdirected grants have been suppressed.
 9. The method of claim 8, furthercomprising: generating the bandwidth map every predetermined period oftime; and outputting the bandwidth map every predetermined period oftime.
 10. A device, comprising: at least one processor configured to:receive, from at least one of a plurality of optical network units(ONUs), a response to the open contention-based grant; determine whethera collision has occurred in response to the open contention-based grant;and provision grants to ONUs in response to determining that a collisionhas occurred wherein when provisioning, the at least one processor isconfigured to at least one of: increase a frequency of open-contentionbased grants for a period of time after the collision occurred, orprovide directed grants to selected ONUs for the period of time afterthe collision occurred.
 11. The device of claim 10, wherein theprovisioning grants causes the at least one processor to: increase thefrequency of open-contention based grants for the period of time afterthe collision occurred.
 12. The device of claim 10, wherein theprovisioning grants causes the at least one processor to: increase thefrequency of open contention-based grants for the period of time, andprovide directed grants to selected ONUs for the period of time.
 13. Thedevice of claim 10, wherein the provisioning grants causes the at leastone processor to: provide directed grants to selected ONUs based on apriority associated with the selected ONUs, wherein the selected ONUsinclude ONUs whose directed grants have been suppressed.
 14. The deviceof claim 10, wherein the provisioning grants causes the at least oneprocessor to: provide directed grants to selected ONUs based on types ofservices provided to end devices coupled to the ONUs or applicationsexecuted by the end devices coupled to the ONUs.
 15. The device of claim10, wherein the at least one processor is further configured to:determine that a collision has occurred, determine whether the collisionhas been cleared, and at least one of: decrease a frequency ofopen-contention based grants for future periods of time after thecollision has been cleared, or suppress directed grants to selected ONUsin response to determining that the collision has been cleared.
 16. Thedevice of claim 10, wherein the at least one processor is furtherconfigured to: generate a bandwidth map, wherein the bandwidth map isbased on whether a collision has occurred and a list of ONUs for whichdirected grants have been suppressed, generate the bandwidth map everypredetermined period of time, and broadcast the bandwidth map everypredetermined period of time.
 17. The device of claim 10, wherein thedevice comprises an optical line terminal channel termination device.18. A non-transitory computer-readable medium having stored thereonsequences of instructions which, when executed by at least oneprocessor, cause the at least one processor to: receive, from at leastone of a plurality of optical network units (ONUs), a response to anopen contention-based grant; determine whether a collision has occurredin response to the open contention-based grant; and at least one of:increase a frequency of open contention-based grants in response todetermining that a collision has occurred, or provide directed grants toselected ONUs based on priority information associated with the selectedONUs in response to determining that a collision has occurred.
 19. Thenon-transitory computer-readable medium of claim 18, wherein theinstructions further cause the at least one processor to: increase thefrequency of open-contention based grants for a period of time after thecollision occurred.
 20. The non-transitory computer-readable medium ofclaim 18, wherein the instructions further cause the at least oneprocessor to: provide directed grants to the selected ONUs based on thepriority information associated with the selected ONUs.